Batch intermediate product yield

The final yield, and any significant intermediate yield, of each production batch should be recorded and checked against the theoretical yield. In the event of a significant variation, steps should be taken to prevent release or further processing of the batch (or of any other associated batches or products processed concurrently, and with which it may have become admixed) until an adequate explanation can be found which does not prevent release or further processing. 

For the situation in which each of the series reactions is irreversible and obeys a first-order rate law, eqnations (5.3.4), (5.3.6), (5.3.9), and (5.3.10) describe the variations of the species concentrations with time in an isothermal well-mixed batch reactor. For consecutive reactions in which all of the reactions do not obey simple first-order or pseudo first-order kinetics, the rate expressions can seldom be solved in closed form, and it is necessary to resort to numerical methods to determine the time dependence of various species concentrations. Irrespective of the particular reaction rate expressions involved, there will be a specific time at which the concentration of a particular intermediate passes through a maximum. If interested in designing a continuous-flow process for producing this species, the chemical engineer must make appropriate allowance for the flow conditions that will prevail within the reactor. That disparities in reactor configurations can bring about wide variations in desired product yields for series reactions is evident from the examples considered in Illustrations 9.2 and 9.3. 

Figure 4.3.6 First-order reactions in series (A l B C) (a) conversion of reactant A and yield of intermediate B and (b) selectivity of the intermediate product B for different ratios of/ci//t2 (cb,o = 0, constant volume, batch reactor). Adapted from Levenspiel (1999).

Figure4.5.29 Influence of external mass transfer on the yield and selectivity of the intermediate product B for a series reaction on a non-porous catalyst In a batch or a plug flow reactor (A B- C) case 1 no Influence of external mass transfer (yS3> (rA,i. =0.1) case 2 influence...

Influence of Reactor Type on Product Yields and Selectivity Let us consider two first-order reactions in series A—C. In batch and plug flow reactors, the yield of intermediate B is given by Eq. (4.3.39), derived in Section 4.3.2.1 ... 

Production of multi-kg batches was originally carried out with extrads of P pastoris overexpressing the modified phenylalanine dehydrogenase from T. intermedius and endogenous formate dehydrogenase. The reductive amination process was further scaled up using a preparation of the two enzymes expressed in single recombinant E. coli. The amino add 105 was direcdy protected as its Boc derivative without isolation to afford intermediate 103. Yields before isolation were dose to 98% with 100% ee [190]. 

Suppose we perform an organic synthesis in a batch reactor where the desired molecule is the intermediate and not the end product. It is then very important that we know how long we should let the reaction run to obtain the highest yield of the intermediate. Setting the differential d[I]/dt in Eq. (99) equal to zero and substituting Eq. (102) into Eq. (99) we find the time, at which the maximum is reached - and by inserting Wx in Eq. (102) the corresponding optimal concentration of the intermediate ... 

Optimal for single-hatch operation. For the sake of simplicity suppose that (1) the performance of an equipment unit is the fraction of the feed material converted to the material that is suitable for the next stage (e.g. the yield of the desired intermediate or final product), and (2) that the objective function is the amount of suitable material produced per unit time. Let us consider the situation shown in Fig. 7.4-5. On completion of cleaning at time ta processing of a batch begins. This processing is characterized by the performance curve/(r), e.g. the yield or conversion versus time relationship. The objective function F is defined as ... 

Keller (1998) describes the semi-continuous reaction process of a vinyl ketone K with lithium acetylide LA to yield lithium ethinolate LE an intermediate in the vitamin production. In an undesired side reaction an oligomer byproduct BP is produced. During the process, reactant K is fed to the semi-batch reactor at a rate to maximize the selectivity for LE. 

As the intermediate is frequently the desired reaction product, this rule allows us to evaluate the effectiveness of various reactor systems. For example, plug flow and batch operations should both give a maximum R yield because here there is no mixing of fluid streams of different compositions. On the other hand, the mixed reactor should not give as high a yield of R as possible because a fresh stream of pure A is being mixed continually with an already reacted fluid in the reactor. 

Another example of cross-aldol condensation is the reaction between citral and acetone, which yields pseudoionone, an intermediate in the production of vitamin A. Noda et a/.[56] working at 398 K with a 1 1 molar ratio of reagents and 2 wt % of catalyst, obtained high conversions (98 %) with selectivities to pseudoionone close to 70 % with CaO and an Al-Mg mixed oxide catalyst these pseudoionone yields are greater than those reported for the homogeneous reaction. MgO exhibited poor activity, and under these conditions only 20 % citral conversion was obtained after 4 h in a batch reactor. Nevertheless, Climent et a/./571 working with 16 wt % MgO as a catalyst, a molar ratio of acetone to citral close to 3 and at 333 K, achieved 99 % conversion and 68 % selectivity to pseudoionone after 1 h. 

Microreactors provide a safe means by which reactions, including multistage schemes, can be undertaken where, otherwise, products involving unstable intermediates may be formed. This is exemplified by Fortt who showed that for a serial diazonium salt formation and chlorination reaction performed in a microreactor under hydrodynamic pumping, significant yield enhancements (15-20%) could be observed and attributed them to enhanced heat and mass transfer [77]. This demonstrates the advantage of microreactor-based synthesis where diazonium salts are sensitive to electromagnetic radiation and static electricity, which in turn can lead to rapid decomposition. Microreactors facilitate the ability to achieve continuous-flow synthesis, which is often not possible with conventional macroscale reactors and batch production. 

Anisole acetylation, which was one of the main reactions investigated, was first shown to be catalysed by zeolite ten years ago by Bayer (13), which was confirmed by Harvey et al. (14), then by Rhodia (15). Large pore zeolites and especially those with a tridimensional pore structure such as HBEA and HFAU were found to be the most active at 80°C, in a batch reactor with an anisole/acetic anhydride molar ratio of 5 and after 6 hours reaction, the yield in methoxyacetophenone (MAP) was close to 70% with HBEA and HFAU zeolites, to 30% with HMOR and 12% with HMFI. With all the zeolites and also with clays and heteropolyacids, the selectivity to the para-isomer was greater than 98%, which indicates that this high selectivity is not due to shape selective effects but rather to the reaction mechanism (electrophilic substitution). The lower conversion observed with HMOR can be related to the monodimensional pore system of this zeolite which is very sensitive to blockage by heavy secondary products. Furthermore, limitations in the desorption of methoxyacetophenone from the narrow pores of HMFI are probably responsible for the low activity of this intermediate pore size zeolite. 

Before committing resources and expensive chemicals to scale-up operations, examine the components of the reaction to ensure that processing proceeds as expected and affords the product in the expected yield and quality. Reaction components include all chemicals to be used in processing starting materials, reagents, solvents, and the chemicals, water, and adsorbents used in work-ups. Different grades of reagents and solvents, different lots of commercial materials, and different batches of intermediates may all need to be qualified. There are basically two approaches to analyze the materials and to perform a use-test. 

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